This invention is concerned with polymer-propellant compositions that are capable of forming foamed structures containing open and/or closed cells from which an aqueous solution can be expressed. Similar compositions have been described by Spitzer et al U.S. Pat. Nos. 3,912,665,-6,-7, patented Oct. 14, 1975. These earlier compositions suffered from a number of disadvantages including the difficulty of preparation and the narrow temperature range over which coherent foamed structures could be obtained.
A practical procedure for preparing polymer-propellant compositions that are capable of forming foamed structures containing open end/or closed cells is described by Osipow, et al in U.S. Pat. 4,328,319. This process comprised coating the synthetic polymer in particulate form with an inert solid material insoluble in the propellant.
Spitzer, et al in U.S. Pat. No. 4,422,877 described synthetic polymer-liquified propellant compositions capable of forming a cold foamed structure having a temperature at least 30 C. below the ambient temperature at which the cold foamed structure is formed, which contain from 50 to 90% be weight of propellant having a heat of vaporization of at least 55 calories per gram, and at least one liquified propellant boiling below -10 C.